Many project artifacts (e.g. WAR, EAR) should only be created once and then get installed at different customers, stages, etc They need to target those different execution environments without necessity of any repackaging. In other words: depending on the situation they need different configuration.
This is easily achievable by having a set of default configuration values inside the project artifact. But be able to overwrite those default values from external.
This very configuration approach has it’s roots in the Apache OpenWebBeans internal SPI configuration. In 2010 it got moved over to the Apache MyFaces CODI project and enhanced to also fit the need of customer projects by Gerhard Petracek and Mark Struberg. In 2011 we further enhanced it while moving CODI to the Apache DeltaSpike project. Romain Manni-Bucau (Apache/Tomitribe), Ron Smeral (JBoss) and Anatole Tresch also gave appreciated input in the last years.
A 'Configuration' consists of the information collected from the registered javax.config.spi.ConfigSource s.
These `ConfigSource`s get sorted according to their ordinal.
That way it is possible to overwrite configuration with lower importance from outside.
By default there are 3 default ConfigSources:
-
System.getenv()(ordinal=400) -
System.getProperties()(ordinal=300) -
all
META-INF/java-config.propertiesfiles on the ClassPath. (ordinal=100, separately configurable via a config_ordinal property inside each file)
That means that I can put my default configuration in a META-INF/java-config.properties anywhere on the classpath.
And I can later simply e.g set a system property to change this default configuration.
It is possible to write and register custom ConfigSource s.
An example would be a ConfigSource which gets the configured values from a shared database table in a cluster.